Democratic nominee Hillary Clinton looks at her mobile phone as she leaves her house to attend Congressional Black Caucus Foundation's Phoenix Awards Dinner at the Washington convention center in Washington, U.S., September 17, 2016. REUTERS/Carlos Barria

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NEW YORK (Reuters) - The Clinton Foundation warned donors about targeted hacking attempts to steal donors' personal information, according to two contributors and a copy of an email seen by Reuters, in a year that has seen an unprecedented wave of hacks of U.S. political organizations.

While the New York-based charitable organization reiterated previous statements that it has "no evidence that our system was breached," it said in its email on Wednesday that hackers were trying to obtain information from donors with fraudulent emails claiming to be from the foundation.

The foundation's email went out about a month before the Nov. 8 general election, in which a number of hacks have played outsized roles in the contest between Democrat Hillary Clinton and Republican Donald Trump.

"I'm writing because it has come to our attention that some Foundation donors have received emails saying their Foundation account information has been hacked, and seeking to confirm personal information via a linked website," according to the email to donors dated Oct. 5 and signed by Danielle Stilz, the organization's chief development officer.

"This email is not from the Clinton Foundation – it is a phishing attempt," she added, offering to answer questions about the authenticity of emails to donors with doubts.

Phishing can involve a fake email or website crafted to look like it is from a legitimate institution, asking recipients to provide personal information.

The foundation did not respond to requests by Reuters to authenticate its email or for comment about the phishing email, whose formatting appeared to match that of the organization's emails and included the same reply-to address as a separate, legitimate email to donors.

Last summer, a wide-ranging hack of the Democratic Party led to the resignations of several senior officials at the Democratic National Committee, after a damaging collection of party emails came to light.

The Democratic Congressional Campaign Committee was also targeted in a similar incident.

On Tuesday, the hacker Guccifer 2.0 tweeted that he had publicly posted data hacked from the Clinton Foundation, but both the foundation and other sources inside the Democratic Party said the information appeared to be provably false.

Clinton campaign officials and other Democrats have linked the Russian government to the attacks and accused it of trying to influence the U.S. election, charges that Russian officials have denied.

In anther incident, the National Republican Senatorial Committee took down a website on Thursday selling campaign stickers and other political gear after saying it had been targeted by a "skimming operation." A Dutch researcher said the site was among thousands infected with a credit card-stealing virus that sent data to a server in Russia.